Radio apparatus



M. MAG ES RADIO APPARATUS Sept. 12, 1933.

Filed May 29, 1930 Patented Sept. 12,V 1933 ,l ssicE RADIO-APPARATUS Morris Mages, Maywood, ll. Application May 29, 1930. serialrNo. 457,162 9 claims. (01.-179-171) t The invention relates to radio apparatus, and

more particularly to push-pull amplifier systems of the type shown and described rin my co-pending application, Serial No. 420,448, led January 13, 1930.

-A particular object of the invention is to provide means for maintaining predetermined operatingY conditions, or` potentials, in the tubes of push-pull systems having means other than l0 transformers for-coupling the output of a tube topush-pull tubes. Thus, the invention is particularly adapted to be'embodied in push-pull systems to couple the output'of a tube and the push-pull tube directly, or by a combination of resistances and capacities,vv or by' a combination of inductances and capacities. n

A preferred form of the invention is embodied in radio apparatus-which comprises a tube that has its output coupled-directly to push-pull tubes through electrical resistances. The load in the output or plate circuit offthe tube which is coupled to the push-pull tubes is divided into two sections, the voltagelacross one of the sections being applied to the input circuit of one push-pull tubev and the voltage across the other section being appliedto the inputjcircuit of the other pushpull tube. Means is providedv for maintaining predetermined potentials V in the elements of 'the tubes. f

Many other objects and advantagesv will'become apparent as'the following description progresses, lreference being had to the accompanying drawing which is a diagram of radio apparatus embodying the invention y In the accompanying drawing, the invention is disclosed in connection with a radio-receiver comprising a radio frequency amplier, a detector and an audio frequency amplier, but it is to be understood that my invention islimited` to such use only to the extent indicated in theappended claims. y Y Y t Inthe drawing,'10 indicates generally an antenna circuit coupled toa radio frequency ampliiier 11 which is coupled to a detector stage 12, the output ofthe detector stage, 12 being coupled to an audio frequency amplifier 13. The output circuit of audio frequency amplifier 13 is coupled to the secondary winding 14 of an audio frequency transformer 15.V Obviously, vthe sec- 5 ondary winding14 may be connected in the usual manner to a loud speaker, or` the equivalent.

' The detector stage 12 preferably comprises a tube 16 comprising a plate 16a, a` grid 1Gb, a

-. cathode 16e` and aiilament 16d- The' audio frequency vamplifier-13 comprises,lin this instance,

` to the bias voltages and plate currents are deterscreen-grid tubes 17'and 18 and power or output tubes 19 yand 20, the primary windings ofthe audio frequencytransformer 15 beingfincluded inthe plate circuits of the tubes 19 and 20. `Op erating potentials are impressed upon the grid, 60 plate and/cathode'elements of the several tubes by means comprising a voltage divider 22.

The output circuit of the detector tube 16 includes resistances 23 and 24 which are preferably substantially equal to each other, the resistance 24 being arranged in parallel with a resistance 25 and a condenser 26, arranged in series.

The plate 16a is connected directly to the control grid of the tube 17 and to one terminal of the resistance 23, the other terminal of the resistance 23 being connected to the voltage divider 22.

One terminal of the resistance 25 is connected to the voltage divider 22 and the other terminal thereof is connected to one plate of the condenser 26 and tothe grid 16h to provide a predetermined bias upon this grid. It will benoted that the grid V16h is included in a tuned circuit andfthat this circuit-is coupled to the output circuit of the radio frequency amplifier 11.

Onev terminal of the resistance 24 is connected 80 to the voltage divider 22 and the other terminal thereof is vconnected to the other plate of the condenser 26 and to oneV terminal of a resistance 30 which has its otherterminal connected to the cathode 16o, the resistance 30 being shunted by ay relatively large condenser 31. That terminal of the resistance 24 which is connected to the condenser`26 is also connected to the control grid of the tube 18.

As described'in more detail in my co-pending application, Serial No. 420,448, the variations in the voltage drop across the resistance 23 are impressed upon the control grid of the tube 17 and the variations in the drop across the resistance '24 are impressed'upon the control grid of o the tube 18, the variations in voltage drops being substantially equal and opposite in phase.

The normaloperating conditions with regard mined in the usual manner by the constants of the circuit, and the primary object of the invention is to provide means whereby any change in these conditions, which the incoming signal tends to produce, is euitornaticallyY prevented. Thusrassuming thatV prior tothe time a signal is impressed upon the antenna circuit, a predetermined bias obtains on the grid 16h, it is readily understood that if a signal is impressed upon the grid the rectified carrier current which will then iiow m the plate circuit` of the tube 1c, in addition to 110 the normal plate current, will cause a larger voltage drop across the resistance 23 and will tend to increase the bias on the control grid of the tube 17 to change it from the predetermined correct bias for that grid. However, there will be a larger voltage drop across the resistances 24 and Si) so that the cathode 16e will become more positive and, therefore, the bias on the grid 1Gb will be increased. This increase of bias on the grid b decreases the plate current so that it returns to substantially its original value, and the bias on the control grid of the tube -17 is returned to its proper value. Of course, the bias of the grid 18 will tend to change in the same manner as the bias on the grid 17 when a signal is impressed upon the antenna circuit 10, but the bias ofthe grid 18 will tend to become more positive when the bias ofthe grid 17 tends to increase, and vice Versa. As a change of this character in the bias of the tube 18 is eiected by an increase of the normal plate current, and such increase of the normal plate current causes an increase in the bias of the grid lbso that the plate current is decreased to its original value, the bias of the tube 18 Willbe returned to its original value.

It may be mentioned at this point in the description that the resistance and condenser 31 may be omitted if it is so desired as the values of the resistances 23 and 24 may be increased. However, the resistance 30 and the condenser 31 are preferably employed so that the constants of the detector circuit are more easily determined.

The apparatus is arranged so that the A. C.

component oi` the signal may vary the bias oi' Veach of the tubes 1.7 and 18 in the usual manner without having its amplitude checked or reduced as is the case with the D. C. component. This is accomplished by preventing the AfC. component from affecting the grid bias of the detector tube. To this end, and as set forth above, the resistance 30 is by-passed by the condenser 3l and the resistance 24 is shunted by the resistance 25 and the condenser 26 in series. The resistance 25 is of a much higher value than the resistance 2e and the condenser 26 is suiciently large so that it comprises a very small part of the total impedance of the shunt circuit. Since the grid bias of the detector is in effect the voltage between the cathode 16e and that plate, of the condenser 26, which is connected to the resistance 25, it will be seen that the A. C. plate current will have a very small impedance path from the last mentioned plate of the condenser 26 to the cathode, which path comprises the condensers 26 and 3l. The condenser 3l is, of course, relatively large to pass audio frequencies.

The A. C. component will flow in parallel paths through the resistances 24 and 25, but as the resistance 25 is of a much higher-value than the resistance 24, most of it will ilow through the resistance 24 and there will be a large voltage variation,l or voltage drop in the resistance 24. There will also be a relatively large voltage variation, or voltage drop across the shunt circuit which includes the resistance 25'and the condenser 26, but most of it will be across the resistance so that there will be a comparatively small or negligible Variatie-nin voltage across the condenser 26. The smali voltage variation across the condenser 26 added to the correspondingly small voltage variation across the condenser 3l constitute the total variation in grid bias of the detector occasioned by the A. C. component in theplate circuit of the detector.

The tubes 17 and 1S of the first push-pull stage are coupled directly to the tubes 19 and 20, respectively, resistances 33 and 34, respectively, being provided for this purpose.V

Generally I prefer to provide a separate winding 35 on the power pack (not shown) to supply the heater current for the detector tube 16 in order to conform to the manufacturers specifications (as to the maximum voltage between the cathode and heater) as the cathode of the detector tube has a potential with respect toground diierent from that of the other tubes.

It is not necessary that the detector tube be coupled to the first push-pull stage, as an amplifying tube may be coupled to the first push-pull stage in the saine manner as the tube 16 is coupled to the tubes 17 and 13 to obtain like results.V In this case, the effect of the signal need not be considered, the circuit being particularly adapted to maintain correct operating voltages when new tubes are inserted therein. Gf course, the circuit shown in the drawing also compensates for variations in tubes. t i

lhen the grid leak detection is employed and the detector is coupled to the first push-.pull stage, the normal plate current will be decreased by the incoming signal, but the system will function in manner similar to that in which it functions when grid bias detection is employed. When grid ieak detection is employed/the resistance 25` is connected to the voltage dividerZZn'such manner that the grid of the detector isy positive with respect to its cathode.-

The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations should be understood therefrom, but theA appended claims should be construed as broadlyl as permissible in View of the prior art.

What I claim as new, and ldesire Ato secureby Letters Patent, is: f v

l. In amplifying apparatus, a power supply, a push-pull stage comprising two tubes having input circuits;` an output circuit coupled to said input circuits, the load of said output circuit being divided into sections separated by the power l,

supply, the control grid ofeach of said tubes-being subjected'to variationsV in the voltage drop across one of said sections, means for` maintaining the average direct current in saidoutput circuit substantially constantwhen the conditions,A under s which the radio apparatus is operating, vary, and means providing an audio-frequency path in parallel with one of said sections.

2. En amplifying apparatus a power supply, a push-pull stage comprising two tubes having input circuits, anoutput circuit coupled to said input circuits, the load of said output circuit being divided into sections separated by the power supply, the control grid of each of said tubes being subjected to variations in the voltage drop across one of said sections, means subjected to the direct current component in said output circuit for preventing sustained fluctuations in the control grid potentials of said tubes, and means providing an audio-frequency path in parallel with one of said sections.

3. In amplifying apparatus, a power supply, .a

, tube having a control grid and a plate and input and output circuits, respectively, connected to said grid and plate,v said output circuitbeing divided into sections separated by the power supply, a push-pull stage having tWo tubes provided with input circuits, one of the last mentioned input circuits being subjected to voltage variations across oneof said sections and the other being subjected to voltage variations across another of said sections,and means including means forming an audio-frequency path in parallel with one of said sections for maintaining the average direct plate current substantially constant under varying operating conditions.

4. In amplifying apparatus, a power supply, a tube having a control grid and a plate, and input and output circuits, respectively, connected to said grid and plate, said output circuit being divided into sections separated, by lthe power supply, a push-pull stage having two tubes provided with input circuits, one of the last mentioned input circuits being subjected -to voltage variations across one of said sections and-the other being subjected to voltage variations acrossV another of said sections, and means including a condenser and a resistance connected in series and forming an audio-frequency path in parallel with one ofrsaid sections for maintaining the direct plate current in said output circuit substantially constant under varying operating conditions.

5. In amplifying apparatus, a power supply, a tube having a control grid anda plate, and input and output circuits, respectively, connected to said grid and plate, said output circuit being divided into sections separated by the power supply, a push-pull stage having two tubes provided with input circuits,kone of the last mentioned input circuits being subjected to voltage variations across one of said sections andthe other being subjected to voltage variations across another of said sections, and means including a condenser and a resistance connected in series and forming an audio-frequency path in parallel with one of said sections for maintaining the direct 'plate current in said output circuit substantially constant under varying operating conditions,\one terminal of said condenser being connected to said grid.

6. In amplifying apparatus, a power supply, a tube having plate, grid and cathode elements, and

input and output circuits operatively connected thereto, the impedance of the output circuit being divided into sections separated by the power supply, Ya resistance in parallel with one of said sections and having one of its terminals connected to one end of said load section through a condenser by-passing audio-frequencies, said terminal of said resistance being connected to said input circuit, and a push-pull stage comprising two tubes having input and output circuits, one of the last mentioned input circuits being subjected to voltage variations in one of said load sections and the other being subjectedto voltage variations in another of said load sections.

'7, In amplifying apparatus, a power supply, a push-pull stage comprising two tubes having inthe proper phase relationship for push-pull op-k eration, and a shunt circuit around one of saidA sections, the control grid of said third tube being connected to an intermediate point on said shunt circuit dividing the impedance of said shunt circuit into two portions, whereby for the audio frequency signals being transmitted, the impedance betweenthe cathode end of the last mentioned section and said point is low compared kto the impedance between said point and the other end of the last mentioned section.

Y 8. In an electrical circuit for transmitting signals, a repeating tube having input and output circuits with a load and a shunt circuit for said load common to said input and output circuits, said shunt circuit consisting of a plurality of sections having impedances differing widely in Value as far as audio frequencies are concerned, the section having the smaller impedance providing an audio frequency path of low impedance in said input circuit, which path shunts said load and the other section so that said input circuit is not subjected appreciably to the degenerative action ofv the signal voltage across said load, and a second tube having input and output circuits, theinput circuit of saidsecond tube including said loadand being subjected to the signal voltage across said load, and the output circuit of` said second tube` being adapted to operate means responsive to said signals.

9. In an electrical circuit for transmitting signals, a repeating tube having input and output circuits with a load and a shunt circuit for said load common to said input and output circuits, said shunt circuit consisting o f a plurality of sections having impedances differing widely in value as far as audio 'frequencies are concerned, the section having `the smaller impedance being adapted` to block direct current and providing an audio frequency pathY of low impedance in said input circuit, which path shunts said load and* the other section so that said input circuit is not subjected appreciably to the degenerative action of the signal voltage across said load, and a second tube having input and output circuits, the

input circuit of'said second tube including said load and being subjected to the signal voltage across said load, and the output circuit of said second tube being adapted to operate means responsive to said signals.

' MORRIS MAGES. 

